Interrupter device for high voltage direct current

ABSTRACT

The overvoltages, occurring on the opening of circuit-breakers, are limited by successively inserting a series of resistances into the line to be broken, the residual current, at the time of the final break, being transferred to capacitors. Each of the preliminary circuit-breaker (D1 or D2) is associated with a resistance (R1 or R2) to be inserted and with a capacitor (C1 or C2), each of said capacitors being connected at two points of the circuit which are situated one at each side of the associated preliminary circuit-breaker (D1 or D2) and the final circuitbreaker (D3).

United States Patent 11 1 1111 3,777,178

Gratzmuller Dec. 4, 1973 541 INTERRUPTER DEVICE FOR HIGH 3,660,723 5/1972 L611 et al. 317/11 0 VOLTAGE DIRECT CURRENT Jean Louis Gratzmuller, 66 Boulevard Maurice Barres, Neuilly, France Filed: 061. 2, 1972 Appl. No.: 294,293

Inventor:

Foreign Application Priority Data Sept. 30, 1971 France 7135198 References Cited UNITED STATES PATENTS 2/1972 Lian et al 317/11 C Primary Examiner-Herman J. Hohauser AttorneyHolman & Stern [57] ABSTRACT The overvoltages, occurring on the opening of circuitbreakers, are limited by successively inserting a series of resistances into the line to be broken, the residual current, at the time of the final break, being transferred to capacitors. Each of the preliminary circuitbreaker (D or D is associated with a resistance (R or R to be inserted and with a capacitor (C or C each of said capacitors being connected at two points of the circuit which are situated one at each side of the associated preliminary circuit-breaker (D or D and the final circuit-breaker (D 4 Claims, 4 Drawing Figures The present invention relates to an interrupter device for high voltage high intensity direct current, especially for the purpose of interrupting lines in a direct current supply system.

It is known that, due to the ever-increasing excessively high voltages employed especially in power system feeder lines, the problem of operational overvoltages, that is to say overvoltages which occur on the opening of circuit breakers, is becoming more and more acute. All the insulating gear, for example line insulators, must be over-dimensioned in order to allow for transient overvoltages which may reach values several times that of the rate operating voltage, unless special precautions are taken to limit these. This problem is referred to as insulation co-ordination.

The practice is known of limiting switching overvoltages by successively inserting a series of resistances which are preferably non-linear and of increasing values. In this case, instead of effecting one single current break, a series of breaks is effected which introduces successive resistances into the line to be broken until the current is sufficiently weak to allow of a final break, in the course of which the residual current istransferred to a capacitor. Unless recourse is had to a large number of breaks in cascade connection (which multiplies the number of circuit-breakers), with such a system, the final capacitor alone receives the totality of residual energy; it must therefore have a considerable capacitance whilst at the same time it must be capable of resisting the total overvoltage. This involves a very expensive type of capacitor which, moreover, is not fully utilised.

It is an object of the present invention to obviate or mitigate such disadvantages by providing interrupter devices for direct current which are more efficient and in which the different elements are better utilised than in conventional apparatus, whereby in fact less expensive installations are made possible.

The general term interrupter device will be employed hereinafter and in the appended claims to designate the entirety of components and circuits placed in a direct current line capableof being interrupted; the term embraces not only the actual interrupter items (for example, circuit-breakers) but also the associated electrical elements such as capacitors, resistances and circuits linking said elements.

According to the present invention there is provided an interrupter device for high voltage high intensity direct current comprising a main circuit containing, in series, a first terminal, a plurality of resistances, a final switching element located between two of the said resistances, and a second terminal, a transfer switching element being associated with each said resistance and being connected to said main circuit on opposite sides of the pertaining resistance, and a capacitor to assist the transfer is associated with at least certain of the transfer switching elements, each said capacitor being connected at two points on the 'main circuit which are situated one at each side of the associated transfer switching element "and the final switchingelement, the arrangement being such that on successively opening said transfer switching elements successively'to insert said resistances the switching overvoltages arereduced.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 shows the circuit diagram of a-first form of interrupter device according to the present invention;

FIG. 2 shows a modified version of the circuit diagram of FIG. 1;

FIG. 3 is a diagram showing the voltages taken at the terminals of an interrupter device according to the invention, for example those shown in FIGS. 1 and 2, and

FIG. 4 illustrates the circuit diagram of a further form a of interrupter device according to the present invention.

Referring now to FIG. 1 the interrupter device for interrupting a direct current line 2 2 between two terminals 4, 6 comprises a main circuit containing, in series between the two terminals 4, 6 a first resistance R a final switching element or circuit-breaker D and a second resistance R the final circuit breaker D being placed between the two resistances and not at the end of the circuit as has been the practice hitherto.

The reistances R R are preferably of non-linear type R being greater in value than R,.

The first resistance R, is connected in parallel with a first transfer switching element or transfer circuitbreaker D whilst the second resistance R is connected in parallel with a second transfer circuit-breaker D A capacitor C C to assist the transfer is connected in parallel with each transfer'circuit-breaker D D but, instead of being simply connected to the terminals of the circuit-breaker with which it is associated, each capacitor is connected at two points on the main circuit which are situated one on each side of the associated transfer circuit-breaker and the final circuit-breaker D Thus, the first capacitor C, has one terminal connected to the point 8 on the main circuit beyond D whilst the second capacitor C2 has one terminal connected to the point 10 before D (the assumed direcn ofs ysm bein sho n t e arrow When the line 2 2 is operational the three circuitbreakers D, D D are closed. In order to interrupt the current, D, D D areopened in turn. When D, is opened, the resistance R is brought intothe circuit, this first intermediate switching operation being assisted by the presence of the capacitorC When D is opened, the second resistance R is brought into the main circuit, this second intermediate switching operation being assisted by the presence of the capacitor C When the final circuit breaker D is opened, the two capacitors C, and C are in parallel, and, furthermore, each is'in series with a resistance (C with R and C with R,), which substantially limits voltage oscillations or absorbs these very rapidly after the final switching operation (see point 14 in FIG. 3).

It will be observed that, the capacitors serve a double purpose, that is to say, they assist the intermediate switching operations and they absorb the residual energy which, after the insertion of the last resistance, is absorbed partly by the set of capacitors and partly by the resistances.

The diagram of FIG. 3 shows the variations in voltage U at the terminals 4 6 of the device in relation to time at themoment of the breaking of current in the device shown in FIG. I. The points of time t, t t

correspond respectively to the opening of the circuit breakers D, D D U is the rated line voltage, and A U is the overvoltage occurring as the circuit-breakers are opened. It will be seen that, after the final switching operation, the voltage at the terminals returns to the rated value U with only a very slight oscillation shown at 14.

In the course of experiments, with insertion of only two resistances (as in the case of FIG. 1 it was possible to limit the overvoltage A U to as low as 0.6 U approximately by suitably selecting the non-linear resistances and the capacitors.

The device illustrated in FIG. 1 has the disadvantage that the entire current passes through the three circuitbreakers D, D D when the line is operational. That is why it is preferable according to the modification shown in FIG. 2, to move the output connection of the first circuit-breaker D to the output terminal 6 of the device. By this arrangement, when the line is operational, the current only passes along the part of the device shown in thick lines, that is to say the circuitbreaker D whilst the circuit-breakers D and D are not subjected to the permanent current. Apart from that, the device functions in identical manner to that described with reference to FIGS. 1 and 3.

More generally speaking, regarding the modification of FIG. 2 it may be said that the switching element D associated with the resistance R,, that is to say the first resistance to be brought into operation, is connected directly between the first terminal 4 and the second terminal 6 of the main circuit, whereby this switching element and the associated conductors are the only parts of the device along which the permanent current passes. This modified lay-out applies equally in the case about to be examined with reference to FIG. 4 in which the breaking of current is effected with the insertion of more than two resistances but the modification is not illustrated in this case.

Although, in most cases, a device having only two resistances (FIGS. 1, 2 and 3) permits of obtaining sufficient limitation of operational overvoltages, the device according to the invention is applicable irrespective of the number of switching stages involved, that is to say of the number of resistances inserted.

Such a device is illustrated by way of example in FIG. 4. In this case the break in current is effected by the successive insertion of four resistances which preferably are non-linear.

The main circuit comprises, in series between the terminals 4 and 6, four resistances R R R R and the final circuit-breaker D which is located between two of these resistances, for example R and R Each resistance is connected in parallel with a transfer circuitbreaker D,, D D D and a capacitor to assist the transfer is associated with each transfer circuitbreaker, the connection being so arranged that each capacitor is connected at two points situated one on each side of the associated transfer circuit-breaker and the final circuit-breaker D For example, the capacitor C associated with the circuit-breaker D is connected on the one hand to the terminal before D and, on the other hand, to a point below D and between R, and R The sequence of operations is identical to that described with reference to FIGS. 1 and 2 and it is sufficient to note that the order of opening of circuitbreakers is: D,,D ,D ,D D It should also be noted that, as in the case of FIGS. 1 and 2, the final circuitbreaker is always placed between two of the resistances instead of being located at one end of the device, as has been the practice hitherto in all known devices for cascade opening of switches with insertion of resistances.

It will now be seen that the invention consists in effecting successive breaks in the course of which the energy is transferred to a series of resistances, each intermediate transfer break being provided with a switching capacitor to assist in breaking the current. The disposition of the switching or interrupter elements, resistances and capacitors is such that, at the moment of the final break, the entirety of capacitors and resistances is utilised to absorb the residual energy; in other words, the capacitors, which are expensive items of plant where high voltages and capacitances are involved, are efficiently utilised.

By virtue of this arrangement, firstly, after insertion of the last resistance, the residual magnetising energy is absorbed partly by the set of capacitors and partly by the resistances; secondly, since each capacitor is in series with a resistance the voltage oscillations after the final break are nil, or at least are very rapidly absorbed. Furthermore, the energetic potential of the capacitors is utilised to the maximum since, at the moment of the final break, these are all in parallel and subjected to the full switching overvoltage, and the value of the resistance associated with each capacitor may, to a certain extent, be selected in order to utilise efficiently the energetic capacitance of the capacitor.

What is claimed is:

1. An interrupter device for high voltage high intensity direct current comprising a main circuit containing, in series, a first terminal, a plurality of resistances, a final switching element located between two of the said resistances, and a second terminal, a transfer switching element being associated with each said resistance and being connected to said main circuit on opposite sides of the pertaining resistance, and a capacitor to assist the transfer is associated with at least certain of the transfer switching elements, each said capacitor being connected at two points on the main circuit which are situated one at each side of the associated transfer switching element and the final switching element, the arrangement being such that on successively opening said transfer switching elements successively to'insert said resistances the switching overvoltages are reduced.

2. An interrupter device as claimed in claim 1, wherein the switching element, associated with that resistance which is the first to be brought into operation, is connected directly between the first terminal and the second terminal of the main circuit.

3. An interrupter device as claimed in claim 1, wherein said resistances are non-linear and successively introduced resistances are of successively greater value.

4. An interrupter device as claimed in claim 2, wherein said resistances are non-linear and successively introduced resistances are of successively greater value. 

1. An interrupter device for high voltage high intensity direct current comprising a main circuit containing, in series, a first terminal, a plurality of resistances, a final switching element located between two of the said resistances, and a second terminal, a transfer switching element being associated with each said resistance and being connected to said main circuit on opposite sides of the pertaining resistance, and a capacitor to assist the transfer is associated with at least certain of the transfer switching elements, each said capacitor being connected at two points on the main circuit which are situated one at each side of the associated transfer switching element and the final switching element, the arrangement being such that on successively opening said transfer switching elements successively to insert said resistances the switching overvoltages are reduced.
 2. An interrupter device as claimed in claim 1, wherein the switching element, associated with that resistance which is the first to be brought into operation, is connected directly between the first terminal and the second terminal of the main circuit.
 3. An interrupter device as claimed in claim 1, wherein said resistances are non-linear and successively introduced resistances are of successively greater value.
 4. An interrupter device as claimed in claim 2, wherein said resistances are non-linear and successively introduced resistances are of successively greater value. 